1. Field of the Invention
The present invention relates to a silent chain, and more particularly to such a silent chain which is constructed to diminish wear elongation of the chain.
2. Description of the Related Art
As shown in FIGS. 3 and 4, a conventional silent chain A1 is composed of a large number of link plates A4 which are articulately connected together in an endless fashion by means of plural sets of rocker pins A2, A3 with each set being constituted by two rocker pins. Teeth of a sprocket A5 come into direct meshing engagement with engaging surfaces T of the link plates A4 to perform transmission of power between the sprocket A5 and another sprocket (not shown).
The link plates A4 are arranged in many rows in the transverse direction of the silent chain A1 in such a manner that the link plates A4, which are adjacent to each other back and forth in the traveling direction of the silent chain A1, are sandwiched alternately in the transverse direction.
Of the two rocker pins A2, A3 which constitute each set, one rocker pin A2 is longer than the other rocker pin A3 and has opposite ends fitted into non-circular pin holes formed in guide plates A6 which are arranged adjacent both outsides of the plural, transversely arranged link plates A4 and are guided by side faces of the teeth of the sprocket A5.
As shown in FIG. 5, the rocker pins A2, A3 have the same cross-sectional shape and are inserted into each of the pin holes A7 and A8 through the link plates A4 so as to be opposed to each other so that respective rocker surfaces R of the rocker pins A2, A3 are adjacent to each other.
The rocker pins A2, inserted into the pin holes A7, A8 of each link plate A4 and located closer to the outer end of the link plate A4, each have a concavely arcuate load-bearing surface C1 formed on the side opposite to the rocker surface R and a pair of convexly arcuate load-bearing surfaces C2 formed on both sides of the load-bearing surface C1. The concavely arcuate load-bearing surface C1 and the convexly arcuate load-bearing surfaces C2, C2 come into engagement with a convexly arcuate pin-seating surface S1 and a pair of concavely arcuate pin-seating surfaces S2, S2, respectively, of each pin hole A7, A8 of the link plate A4 so that the rocker pins A2 are prevented from rotating.
The load-bearing surface C1 and each of the load-bearing surfaces C2, C2 are smoothly connected together by a convexly arcuate surface having a small radius of curvature r1 (FIG. 5A). The pin-seating surface S1 and each of the pin-seating surfaces S2, S2 are smoothly connected together by a concavely arcuate surface having a radius of curvature r2 (FIG. 5A) which is slightly smaller than the radius of curvature r1. Due to the different radii of curvature r1 and r2, the convexly arcuate surface and the concavely arcuate surface are spaced by a slight gap or clearance.
On the other hand, the rocker pins A3 inserted into the pin holes A7, A8 of each link plate A4 and located closer to the center of the link plate A4, are each engaged at respective load-bearing surfaces C1 and C2 with pin-seating surfaces of a corresponding one pin hole formed in a longitudinally adjacent link plate (not shown).
As shown in FIG. 3, when the silent chain A1 is entrained on the sprocket 5 and a tensile force is exerted between longitudinally adjacent link plates A4, the rocker surface R of the rocker pin A2 and the rocker surface R of the rocker pin A3 are pressed against each other to effect transfer of the tensile force.
Since the opposed rocker surfaces R and R are each formed in a convexly arcuate shape, it becomes possible to perform a relative rocking motion between the rocker pins A2 and A3, thus permitting bending or articulating of the longitudinally adjacent link plates A4.
In the conventional silent chain A1 constructed as described above, the convexly arcuate pin-seating surface S1 and the two concavely arcuate pin-seating surfaces S2 of each of the pin holes A7, A8 and the concavely arcuate load-bearing surface C1 and the convexly arcuate load-bearing surfaces C2 of the associated rocker pins A2 which are located closer to the outer ends of the link plate A4 are simultaneously brought into engagement with each other to effect transmission of a tensile force while preventing rotation of the rocker pins A2, A3 relative to the link plate A4.
Form the manufacturing point of view, however, it is vary difficult to finish the rocker pins A2, A3 and the pin holes A7, A8 with high accuracies to secure the afore-mentioned simultaneous engagement between the three surfaces S1, S2, S2 of each pin hole A7, A8 and the corresponding surfaces C1, C2, C2 of the rocker pins A2. In practice, it may occur that due to uneven or local engagement, the rocker pins A2, A3 become wobble within the pin holes A7, A8 which is usually accompanied by local wear. Especially, when the wear is concentrated on the pin-seating surfaces S1 of the pin holes A7, A8 or on the load-bearing surfaces Cl of the rocker pins A2, the wear will progressively grow or increase in the longitudinal direction of the silent chain. This will often result in an increased wear elongation of the silent chain.